Here are people who are said to have played with Jerry who remain un-pinned down in Jerrybase because we don't have enough data specificity. Add more in comments!
Randy Bachman: "he played his fingers raw with Jerry Garcia, Leslie West and Delaney Bramlett" on the Festival Express (xxx citation)
Byron Berline: OAITW, ca. summer 1973 - likely backstage at Whipoorwill Festival in Warrenton, VA. I estimate that Berline and Garcia did not play together. Berline played with "Old And In The Way", which was Grisman, Rowan, Vassar to him. As far as I can recall, there's no evidence of Garcia picking around the grounds or backstage at this festival. I think he coptered up to DC for the Dead shows. Again, none of this is certain to me.
Frank Dardano of Jacob's Ladder (Portland, Oregon) - before March 1972: "We had a chance to jam with the Dead's Jerry Garcia. He's down to earth and not weird or anything. He even showed me how to work out some things on my guitar." -- Sunday Oregonian, 3/5/72
Luis Gasca. I imagine this was at the 9/22/72 United Farmworkers' Benefit.
Donny (or Danny?) Hanna: Orlando based rock guitarist and bassist, bands Power and New Days Ahead. "Hanna has played with Jerry Garcia of the Grateful Dead" (McAleenan 1972).
Bernard Purdie: JGMS Bottom Line 1974, via Big Steve who recalled Kreutzmann drumming. That's not quite right. I actually know about this now and will write about it in Fate Music.
Ike Stubblefield: JGB 1970s
Ross Valory (phantom)
Linda Waterfall (Seattle folk soloist) "has shared a stage with ... Jerry Garcia" -- Daily Astorian, 10/10/82 p 7